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Cory Hussar, Tatiana Pasternak; Dynamic modulation of direction selectivity by task demands in prefrontal cortex. Journal of Vision 2007;7(9):345. doi: https://doi.org/10.1167/7.9.345.
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© ARVO (1962-2015); The Authors (2016-present)
Responses of neurons in the prefrontal cortex (PFC) have been shown to represent behaviorally relevant sensory information. Recent work revealed that PFC neurons exhibit direction selective (DS) responses to visual motion used in a delayed match-to-sample (DMTS) task in which the monkeys compared two directions of motion separated by a brief delay (Zaksas & Pasternak, J. Neurosci, 2006). We asked whether this directionality is preserved when the monkeys were asked to ignore stimulus direction. We compared responses of PFC neurons to identical visual motion stimuli presented during three different tasks. In separate blocks of trials the animals discriminated the direction or the speed of motion, or were rewarded for passively maintaining fixation. We found that DS responses were drastically attenuated under both conditions in which stimulus direction was irrelevant and that the nature of this attenuation was task dependent. When the monkey discriminated stimulus speed and ignored its direction, DS activity was strongly attenuated early in the response and emerged about 100ms later than during the direction discrimination task. This early reduction of DS activity resulted not from a decrease in the response to the preferred direction, but from an increase in the response to the anti-preferred direction, suggesting an active release from inhibition characteristic of direction selectivity in visual cortical neurons. In contrast, during the passive fixation task, reduction in DS activity resulted largely from the decrease in the response to the preferred direction, which unlike the more transient loss in DS during the speed task, persisted throughout the response. Our results demonstrate the existence of a dynamic gating mechanism by which PFC neurons can modulate direction selectivity characteristic of visual cortical neurons.
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